As is known in the art, switching regulators provide a regulated output voltage to a load. The output voltage is regulated to be a substantially constant voltage irrespective of variations in the load and variations in the input voltage.
Conventional switching regulators are provided in at least three configurations, including, but not limited to buck, boost, and buck-boost configurations, each described below. Depending upon configuration, a conventional switching regulator can have one or more switches, and typically either one, two, or four switches. A control circuit, provided to control the switches, forms a part of the switching regulator.
Referring to FIG. 1, a prior art buck switching regulator 10 includes an optional input capacitor 12, two switches A, B, an inductor 16 having first and second ends 16a, 16b respectively, an output capacitor 14, and a control circuit 18 all coupled as shown. A load 24 is coupled to the output of the buck switching regulator 10.
The buck switching regulator 10 is adapted to receive an input voltage Vin and to provide a regulated output voltage Vout that is less than the input voltage Vin. The control circuit 18 provides two control signals VA and VB for controlling switches A and B, respectively. The switches A and B are turned on and off alternately such that switch A is on while switch B is off and vice versa. The term “on”, as used herein, describes a closed switch and the term “off”, as used herein, describes an open switch.
The conventional buck switching regulator 10 has two “states”, i.e. switch conditions. In a first state, switch A is closed and switch B is open. In a second state, switch A is open and switch B is closed. The first and second states can be designated as A and B, corresponding to the closed switches in each state. A regulated output voltage Vout is achieved by controlling the relative time spent in each of the two states, A and B.
One of ordinary skill in the art will recognize that, in an alternate embodiment, a diode (not shown) having a cathode coupled to the first end 16a of the inductor 16 and an anode coupled to ground 13 can replace switch B. In this alternate embodiment, a control circuit, similar to the control circuit 18, provides one control signal VA for turning switch A on and off.
Referring now to FIG. 2, a prior art boost switching regulator 50 includes an optional input capacitor 52, two switches C, D, an inductor 54 having first and second ends 54a, 54b respectively, an output capacitor 56, and a control circuit 58 all coupled as shown. A load 60 is coupled to the output of the boost switching regulator 50.
The boost switching regulator 50 is adapted to receive an input voltage Vin and to provide a regulated output voltage Vout that is greater than the input voltage Vin. The control circuit 58 provides two control signals VC and VD for controlling switches C and D, respectively. The switches C and D, are turned on and off alternately such that switch C is on while switch D is off and vice versa.
The conventional boost switching regulator 50 has two states. In a first state, switch C is closed and switch D is open. In a second state, switch C is open and switch D is closed. The first and second states can be designated as C and D. A regulated output voltage Vout is achieved by controlling the relative time spent in each of the two states C and D.
One of ordinary skill in the art will recognize that, in an alternate embodiment, a diode (not shown) having a cathode coupled to the regulated output voltage Vout, and having an anode coupled to the second end 54b of the inductor 54 can replace switch C of FIG. 2. In this alternate embodiment, a control circuit, similar to the control circuit 58, provides one control signal VD for turning switch D on and off.
Referring now to FIG. 3, a prior art buck-boost switching regulator 90 includes an optional input capacitor 92, switches A, B, C and D, an inductor 94, an output capacitor 96, and a control circuit 98 all coupled as shown. A load 100 is coupled to the output of the buck-boost switching regulator 90.
The buck-boost switching regulator 90 is adapted to receive an input voltage Vin and to provide a regulated output voltage Vout for input voltages Vin substantially equal to the output voltage Vout. The control circuit 98 provides four control signals VA, VB, VC, and VD for controlling switches A, B, C, and D respectively. Switches A and B are turned on and off alternately such that switch A is on while switch B is off and vice versa. Similarly, switches C and D are turned on and off alternately such that switch C is on while switch D is off and vice versa.
The conventional buck-boost switching regulator has two states. In a first state, switches A and D are closed while switches B and C are open. In a second state, switches A and D are open and switches B and C are closed. The first and second states can be designated as AD and BC corresponding to the closed switches in each state. A regulated output voltage Vout is achieved by controlling the relative time spent in each of the two states AD and BC.
One of ordinary skill in the art will recognize that, in alternate embodiments, diodes (not shown) coupled as described above in conjunction with FIGS. 1 and 2 can replace one or both of the switches B and C. In these alternate embodiments, a control circuit, similar to the control circuit 98, provides two or three control signals, rather than the four control signals VA, VB, VC, VD, for controlling the two or three switches.
Another conventional switching regulator, described in U.S. Pat. No. 6,166,527 to Dwelley et al., provides a buck-boost mode for which there are three states, designated as AC, BC and AD, each identifying closed switches during a respective state. In order to provide a regulated output voltage, Dwelley et al. controls duty cycles of the three states AC, BC, and AD, adjusting a period of time spent in each state during each cycle of the switching regulator, where a cycle of the switching regulator will be understood to correspond to a cycle of a periodic waveform associated with the switching regulator.
An important consideration in switching regulator design is efficiency. It will be appreciated by those of ordinary skill in the art that efficiency is lost in a switching regulator when switches, for example switches A, B, C, and D of FIG. 3, change state. This is due in part to capacitance associated with each switch, which causes high frequency components of the control signals to be shunted to ground or elsewhere during transitions of the control signals.
It would, therefore, be desirable to provide a switching regulator having improved efficiency.